The James Webb Space Telescope, a project dating back to the late 1900s, may launch this very century After years of delays, the James Webb Space Telescope may actually launch this year, having passed a "final mission analysis review," we're told. Work began on the space telescope, once called the Next Generation Space Telescope (NGST), in 1996 with a planned launch date of 2007. That slipped almost immediately due to budget …
Now, since James Webb is what they call an "Infra Red" telescope, it will produce pictures nothing like the Hubble, but a range of grey scale in the infra red frequency, which will then will be coloured in by artists, as an impression, like old black and white films...
And critics rave on how much they prefer the colourised stuff...
Still, they will be far higher resolution grey scale than the Hubble does colour...
I don't get the argument about colouring.
E-M waves are a mixture of frequencies. Surely the important scientific information is (the fourier transformation of) that spectrum for each point the telescope can distinguish? The tiny subset of that information that happens to be perceivable by cells in the human eye is almost irrelevant.
I presume that would be much too much information to process, store and communicate down to earth. So, some compromises are made. How does Hubble do image data collection? Does it use RGB and normal graphics formats? With compression? Or does it use more than 3 detectors? or detectors programmable to different frquencies and multiple passes?
And what will James Webb use? If it is infrared it certainly can't be using standard RGB. Is it also using 3 frequencies to look for? Or what?
Whatever the mechanisms, the most important scientific data is presumably in the numbers themselves. But visualising them can be useful for both scientists and the public at large. There can be no expectation that the visualisations use accurate colours, particularly for the data outside the visible spectrum. But it might be useful if they tended to map the range (red for lowest frequencies, violet for highest).
This post has been deleted by its author
Hubble doesn't take colour photos - they are 'colorized' later on (and not true colours). See: https://petapixel.com/2019/08/02/this-is-how-scientists-colorize-hubble-photos-of-deep-space/
I like this quote from the petapixel article:
[...] the first color images were composites of three black-and-white photographs captured through a red, green, and blue filter, respectively.
Um, what exactly does whoever wrote that think a Bayer (or any other pattern, such as X-trans) sensor does? Because what it does is produce three black-and-white images taken through red, green and blue filters which are then composed to produce a colour image.
The only digital sensor design which might even be considered to produce colour directly is Foveon, but even then it's actually just three B/W images: it's just that the photodiodes are stacked for Foveon (and I think the spectral sensitivities of each layer are not RGB but more complicated spectra.
Foveon of course is just what a color film does.
There are direct color array detectors. Where each pixel measures the energy (ie wavelength) of the incoming photon directly. Unfortunately they generally need to be cooled to a few Kelvin and so are inconvenient in a cell phone.
If you're just interested in spectacular images of very distant objects, you're probably OK no matter what happens with the Webb observatory. Several large earth bound telescopes with mirrors approaching the size of a soccer field are scheduled to come on line in the next decade. What Webb will give you that they won't (I think) is well resolved false color images of cooler objects radiating at wavelengths longer than the visible spectrum.
I need something astronomical to fill the void
Gaia. If anything has/will transform astronomy it is ESA's Gaia. It's third data release due soon.
A stunning achievement that has already exceeded expectations, and is feeding in to so many different areas.
ESA's Gaia archive
Yes, 14 years since the originally pencilled launch date, we're lucky Hubble lasted so long after the last service mission.
I can't remember if the Webb was initially slated to ride a shuttle flight or the (then only a prototype) Ariane-5. Now the shuttles are long gone and the A-5 series is into the last batch of launchers before Ariane-6 appears.
Are there any space boffins now working on the Webb that were born after it's initial announcement in 1996?
I don't think there was ever a decision made on what to launch JWST on but I don't think STS could have put it in the required (transfer) orbit, so it would have needed a kickstage developed just for that purpose. It's current config I think would have fit in the cargo bay so maybe the shuttle could have managed it. Also the shuttle was a notoriously bumpy ride (especially up to SRB separation) so I'm not sure it would have made a good launch vehicle for JWST.
Given the regularity of spy sat launches (which hubble stole some tech from), and now Space X, surely the next gen for this stuff is rapidly build v1.0, throw it up on a Falcon 9 heavy and replace every 3-5 years as they learn from it? Surely that can't be any more expensive than the current all eggs in one basket approach?
No such thing as "rapid" when building space telescopes. It took 4 years just to develop a test demonstrator for a single mirror segment:
https://www.jwst.nasa.gov/content/observatory/ote/mirrors/index.html
Now they have it, things could go faster in the future. Maybe. The mirrors still take a lot of time to grind, for example. Maybe loft a few more JWST-class 'scopes pointing in different directions, if orbital dynamics permit.
But that's just keeping like for like. Going bigger, better, more capable means pushing the envelope still further, which means long leads times, technical demonstrators, designing and trying different approaches.
Yes, more "like for like" scopes doesn't sound so impressive as one new "bigger-er" scope, however... I remember reading about a technology that allows smaller ground-based scopes to be used in concert to effect a large "virtual" mirror, using interferometry and other clever wheezes.
If we can have an earth-bound telescope with a virtual mirror that spans the globe's diameter (and I believe this is either in the works, or is already happening - it's definitely happening with radiotelescopes) then a space-based scope on the same basis (using a handful of JWSTs, or "just" Hubbles) could give provide a truly massive baseline: if the (admittedly daunting) logistics were overcome, using L4 & L5 in the sun/earth system gives a baseline that's around 260 million kilometers.
Which is probably enough to see _something_
(in fact, there are a handful of cube-sat based missions of this sort being planned, so it probably doesn't need to be JWST*n-sized budget either)
The Webb telescope is supposed to fly to the L2 point 1.5 million km out. Technically it will be (if it gets there) in solar orbit, not earth orbit. I'm not sure that Falcon 9 could get it there. Somebody around here probably does know.
It's also huge -- the mirror is 6.5m (21 feet) in diameter. That's larger than all but a handful of earthly telescopes. Building optical devices that size takes monumental effort. Building a new one every 3-5 years would probably take significant chunk out of mankind's space budget which is currently around $70B a year and is largely committed to useful stuff -- e.g. communications satellites, weather satellites and to politically popular but (IMHO) rather pointless manned missions. Personally, I'd rather see the money go to things that will tell us potentially useful stuff -- more lunar and Mars rovers and resource surveys of asteroids.
I'm not an optics nerd, but from my basic understanding of optics and mirror polishing I understand how insanely hard that is.
A spherical mirror that large is a challenge, an aspherical mirror at that scale is even more difficult, an off axis parabolic is.... probably feeling like someone's life work.
Can the Falcon launch the JWST?
The F9, no, the FH, yes.
JWST is 6500Kg at launch and requires a C3 (characteristic energy) of -0.7Km2/s2 to get to L2.
The F9 recovering to the droneship can do 3400Kg, the FH can do 6820Kg recovering all three boosters.
So the FH can launch the JWST and recover all three boosters, but with a small margin for any under performance (e.g. loose a Merlin on the way up). I suspect if bidding today it would be an FH and expend the centre booster to give the extra margin which NASA love.
My understanding is the A5 launcher is the ESA's buy in to the project to get access to the JWST.
F9 (and FH) fairing isn't large enough for JWST. It CAN'T launch on anything SpaceX is currently offering. (I'm still surprised they haven't built a larger fairing for Falcon Heavy. You need something pretty dense to make use of the deltaV it offers. And it seems it should have more than enough control authority to be able to handle a larger fairing without losing too much crosswind margin.)
I subscribe to "Inbox Astronomy", which touches on things interestingly astronomical. Many times, the articles will be about the James Webb telescope, and what it will be used for.
Don't tell me what it WILL do, show me what it CAN do.
Especially in these times that it may be "Adieu pour toujours" for the HST.
L2 is unstable so nothing stays there without station-keeping. The amount of fuel you need to expend goes, I think, quadratically with the distance from L2 (for short distances), so I imagine it will stay as close as it possibly can. The only thing that might prevent that, that I can see, is other spacecraft which it wants to keep away from: nothing natural sits at any of the unstable Lagrange points (1, 2 & 3) for obvious reasons.
It's never going to the exact L2 point, but to what is called a "halo orbit". It will be oscillating/circling around the L2 point. Since this is not exactly stable it will probably require around 4 to 5 m/s of deltaV every year to stay close enough (There's roughly 150 m/s of fuel available after launch and orbit insertion)
Wow, to think that something could be so ... last century! Well, in CPU years it was a long time ago, but no, not really that long ago.
Yeah, great to think that the telescope might finally make it to orbit. Of course, if 10 beeelion dollars were spent on a ground telescope, it would be really great, except for the clouds of microsatellites obscuring the view. Who knew we would lose the stars just to watch cat videos...
The most recent causes of delay related not to the JWST but to the Ariane 5 launch vehicle. There have been issues with the payload fairing and it was grounded until July and it will have to have two successful launches before it is certified for the JWST launch.
Interesting note - the JWST could be flown to French Guiana but the bridges between the airport and the launch site wouldn't hold its weight so it's being shipped. sometime this summer. The date may not be announced because of the fear of piracy (yes,really).
The Register 
Biting the hand that feeds IT
Copyright. All rights reserved © 1998–2024
